A magnetoresistive magnetic head is used as a read sensor in the field of high-density magnetic recording techniques centered around hard discs. It largely affects the performance of the magnetic recording techniques. As the recording density of magnetic recording apparatuses is rapidly growing higher, it is difficult, using conventional techniques, to realize a magnetic recording apparatus with an adequately high recording density. Particularly, it is difficult to realize a magnetoresistive magnetic head which, having adequate sensitivity and output capacity usable in working on an external field, can be used in the read section of a magnetic recording apparatus and which achieves an adequately stable and good characteristic. Hence, with conventional techniques, it has been difficult to realize functions required of a storage device.
It has been known for years that the magnetoresistive effect of a multilayered film including ferromagnetic metallic layers stacked via a non-magnetic metallic layer, i.e. so-called giant magnetoresistance (GMR), is great. Conventionally, when making use of a magnetoresistive effect for a magnetic head, a so-called CIP-GMR (Current in-plane Giant Magnetoresistive) sensor in which an electric current flows in the plane of the multilayered film used to be adopted. In addition to the CIP-GMR sensor, a tunneling magnetoresistive sensor and a current-perpendicular-to plane giant magnetoresistive sensor, i.e. the so-called TMR sensor and CPP-GMR sensor in which an electric current flows in the film thickness direction of a multilayered film, are currently being studied. These types of sensors are applied to magnetic heads after being patterned into a predetermined size and shape. With regard to their shape, their track width is of a particular importance. Because the track width of a sensor determines the spatial resolution of the sensor, reading high-density magnetic data requires a head with a small track width to be fabricated. The known sensor shapes in the track width direction can be broadly classified into the following three types: a first type in which the side walls of the track are formed linearly; a second type in which the track width is smaller in an upper portion of the element than in a lower portion of the element; and a third type in which the element has side walls which are upwardly concavely curved. Typical sensor shapes of the above types and methods for forming them are described, for example, in Japanese Laid-Open Patent No. JP 2003-332651 (patent document 1), Japanese Laid-Open Patent No. 2004-319060 (“patent document 2”), and Japanese Laid-Open Patent No. 2002-9285 (“patent document 3”). In the Japanese Patent Publication No. 2005/0045580 (“patent document 4”), a sensor fabrication method in which side walls of a track are ion beam etched in plural steps at different incident angles (incident angle ranges of 0 to 30 degrees and 65 to 90 degrees are cyclically repeated) is described.
Conventional types of magnetoresistive sensors have a read section formed of a magnetoresistive multilayered film. Typical examples of such magnetoresistive sensors include GMR films. New types of magnetoresistive multilayered films such as TMR and CPP-GMR films, have also been proposed. In forming a magnetoresistive sensor using one of such films, the magnetoresistive film is formed into a predetermined size in photoresist and etching processes, so as to obtain required magnetic and magnetoresistive characteristics. FIG. 1 shows an example of the shape of a CPP type magnetoresistive sensor as viewed from the side to face a recording medium. As shown in FIG. 1, a seed layer 25, an anti-ferromagnetic film 24, a pinned layer 23, an intermediate layer 22, a free layer 21, and an upper electrode layer 239 are stacked over a lower electrode layer 240, and an insulator layer 12 and a domain control layer 131 are formed on sides of the element. The width perpendicular to the film thickness direction of the free layer 21 is regarded as the track width. The inclination of the side walls of the track is formed by etching, such as ion beam etching or reactive ion beam etching, using the resist formed on the element by photolithography as a mask. Ion beam etching is performed as shown in FIG. 2, using a resist 3 formed over a magnetoresistive sensor 14 as a mask. During etching, magnetoresistive film fragments removed from the magnetoresistive film bombarded by argon ions (irradiated with argon ions) may redeposit on the side walls being etched. If, after the element has been formed, the redeposition is left on the side walls, an electric current flows through the redeposition whose electric resistance is lower than that of the magnetoresistive sensor. This degrades the magnetoresistive effect of the element.
The damage suffered by the magnetoresistive sensor when irradiated with argon ions in an etching process can also degrade the magnetoresistive effect of the element. When the side walls of the magnetoresistive sensor are bombarded by argon ions during etching, crystals in the vicinity of the side walls or portions of a tunneling barrier layer and an intermediate layer in the vicinity of the side walls may be deteriorated. When the track width of an element is smaller, a relatively larger area of the element is affected by etching. This increases the influence of characteristic degradation. To prevent such characteristic degradation of a magnetoresistive sensor, forming the element such that its side walls are gently inclined as described in the patent document 4 is considered effective. Because, when the side walls are inclined, ion beam etching performed to form the element into a predetermined width also serves to remove the redeposition on the side walls. Such a method, however, lowers the accuracy of the sensor track width because it is geometrically difficult to specifically define the width of a track, particularly, the width of a free layer having gently inclined side walls.
Thus, the conventional techniques pose a problem. Namely, forming the side walls of a magnetoresistive sensor to be vertical or nearly vertical so as to improve the width accuracy results in characteristic degradation, and forming the side walls to be inclined so as to prevent characteristic degradation lowers the width accuracy. It has therefore been difficult to develop and mass-produce high-output sensors with a small track width.
Furthermore, in cases where lift-off is performed by CMP (chemical mechanical polishing) to form a small magnetoresistive sensor, there have been concerns that oxide layers of the element, for example, tunnel gap and current confining structures, may be damaged, thereby decreasing the output capability of the element.